1. Field of the Invention
The present invention relates to a self-heating container using an exothermic reaction agent for heating a contained liquid foodstuff such as soup and coffee, or solid and semi-solid foodstuffs such as cooked cereals, vegetables and meat, without a supply of external thermal energy.
2. Description of the Prior Art
Various types of self-heating containers are known for heating contents (mainly foodstuff) by heat of hydration between an exothermic reaction agent such as quicklime and water, as disclosed, for example, in Japanese Patent Publication No. 57-54382. The self-heating container disclosed in this publication includes a foodstuff and an exothermic reaction agent, and has at the top thereof an opening covered with a seal which can be removed when desired so that water can be poured through the opening over the exothermic reaction agent. However, this container involves not only a danger of erupting hot steam from the opening due to hydration but also a disadvantage that water has to be carried along when it is used outdoors.
Another type of a self-heating container is disclosed in U.S. Pat. No. 3,970,068 and includes a bag filled with water for use in the hydration reaction. When in use, the bag is ruptured with a needle member so that water may come out to mix with the exothermic reaction agent. However, the hole bored by the needle member is too small to pass a sufficient amount of water for the initial hydration, so that water does not diffuse completely through the exothermic reaction agent. Therefore, a large part of the exothermic reaction agent tends to remain unreacted, resulting in that foodstuff is not heated to a desirable temperature. Particularly in the case quicklime is used as an exothermic reaction agent, when an amount of water supplied to quicklime per unit time is short at the initial stage of reaction, hydrated lime near the hole absorbs a substantial amount of water discharged through the hole so that only a relatively small amount of quicklime near the hole effects hydration. Accordingly, this container is not suitable particularly for a solid or semi-solid foodstuff which requires a substantial amount of thermal energy of heating.
It is therefore an object of the present invention to provide a self-heating container which enables sufficient hydration between an exothermic reaction agent and water and may generate thermal energy efficiently.
It is another object of the present invention to provide a self-heating container suitable for a solid or semi-solid foodstuff which requires a substantial amount of thermal energy for heating.
It is still another object of the present invention to provide a self-heating container of relatively simple structure which may be produced at a low cost, and yet which is suitable for mass production.